Distributed antenna systems (DAS) can be used in confined areas to deploy wireless coverage and capacity to mobile devices. A DAS can include active elements such as master units, extension units, and remote units. Among the variety of active elements, a typical DAS may include passive elements as well. Examples of such passive elements are: coaxial cables, RF splitters, RF combiners, RF antennas, optical fiber, optical splitters, optical combiners, attenuators, dummy loads, cable feeds, and surge protectors. Other passive RF or optical devices can include connectors, jacks, wall jacks, and patch cords.
Systems are presented for detecting the presence of passive RF or passive optical devices that are present in a DAS. The presence of such device can be facilitated through the employment of radio frequency identification (RFID) chips. One aspect includes coupling the RFID chip to the device that is to be detected. In one aspect of such systems, a coupling network is used to couple to a signal wave inside of a waveguide such as coaxial cable, optical fiber or other type of waveguide. Examples of the coupling network are resonant coupling networks, bandpass filters, low pass filters, high pass filters, and directional or non-directional couplers. One purpose of the coupling network is to pass a maximum of RF energy coming from the interrogator or RFID reader to the RFID chip. Another feature of such systems is that they block other signals used in the DAS at different frequencies than the RF interrogator frequency to avoid potential generation of intermodulation products by the potential non-linear characteristic of the RFID chip.
In such systems, a DAS is provided that includes one or more passive elements. Each passive element can be associated with an RFID chip. The RFID chip may be integrated into the passive element or may be coupled, connected, or otherwise associated with the passive element. A reader may be integrated within or otherwise associated with a sub-system of the DAS that is remote from at least some of the passive elements. The reader can transceive RFID signals over a communications network of the DAS. The communications network may include, for example, coaxial cable or another transmission medium that can carry RF signals and RFID signals through the DAS. For example, the reader may transmit an RFID signal that is carried by the communications network through a coupling network to the RFID chip associated with a passive element.
The RFID chip can respond to the RFID signal with a responsive signal representing an identifier of the passive element. The responsive signal can be received from the coupling network and transported by the communications network to the reader. The reader may extract the identifier from the responsive signal and provide the identifier to a controller. The passive element may not be required to be powered for a reader to detect the presence of the passive element. Both the reader and the RFID chip may be configured to be in a fixed position within the DAS, as opposed to the reader being moveable. In other aspects, the reader includes one or more readers that are moveable.
An RFID chip may be any item that can respond to an RFID signal with a responsive signal representing an identifier for the item. An “RFID chip” may also be known as an “RFID tag.”
One such system is described in U.S. patent application Ser. No. 13/798,517, filed Mar. 13, 2013 and entitled “Detecting Passive RF Components Using Radio Frequency Identification Tags”, which application is incorporated herein by reference in its entirety.
To fully characterize a passive network beyond the active boundaries of a distributed antenna system, additional information is necessary, beyond determining the presence and identification of passive RF devices. The location, physical distance and layout and insertion loss of such elements is desired. Therefore, there is a need for such a DAS system that, in addition to determining the presence and identification of various passive elements in a DAS, can further provide other characteristics and parameters for passive elements in the DAS.